Photochromic polyurethane laminate

ABSTRACT

A photochromic polyurethane laminate that is constructed to solve certain manufacturing difficulties involved in the production of plastic photochromic lenses is disclosed. The photochromic laminate includes at least two layers of a resinous material and a photochromic polyurethane layer that is interspersed between the two resinous layers and which contains photochromic compounds. The polyurethane layer is formed by curing a mixture of a solid thermoplastic polyurethane, at least one isocyanate prepolymer, at least one photochromic compound, and a stabilizing system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/563,985 filed Dec. 8, 2014 entitled Photochromic PolyurethaneLaminate (now U.S. Pat. No. 10,052,849 issued Aug. 21, 2018), which is acontinuation of U.S. patent application Ser. No. 13/645,696 filed Oct.5, 2012 entitled Photochromic Polyurethane Laminate (now U.S. Pat.8,906,183 issued Dec. 9, 2014), which is a divisional of U.S. patentapplication Ser. No. 10/938,275 filed Sep. 9, 2004 entitled PhotochromicPolyurethane Laminate (now U.S. Pat. No. 8,298,671 issued Oct. 30,2012), which claims the benefit of priority from U.S. ProvisionalApplication Ser. No. 60/501,820 filed Sep. 9, 2003 entitled PhotochromicLaminate; and U.S. Provisional Application Ser. No. 60/501,819 filedSep. 9, 2003 entitled Photochromic Film And Method Of Manufacture, allof which are hereby incorporated herein by reference in theirentireties.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to a photochromic laminate thatcan be applied to polymeric surfaces or can be used by itself as aphotochromic element. The invention also relates to a photochromiclaminate that is capable of withstanding high temperatures and can beincorporated into plastic lenses by means of injection molding. Theinvention further relates to a photochromic laminate that is excellentin both control of thickness and surface smoothness of the photochromiclayer, and thereof exhibits uniform darkness at the activated state.

Description of the Related Art

Photochromic articles, particularly photochromic plastic materials foroptical applications, have been the subject of considerable attention.In particular, photochromic ophthalmic plastic lenses have beeninvestigated because of the weight advantage and impact resistance theyoffer over glass lenses. Moreover, photochromic transparencies, e.g.window sheets, for vehicles such as cars, boats and airplanes, have beenof interest because of the potential safety features that suchtransparencies offer.

The use of polycarbonate lenses, particularly in the United States, iswidespread. The demand for sunglasses that are impact resistant hasincreased as a result of extensive outdoor activity. Materials such aspolycarbonate have not historically been considered optimal hosts forphotochromic dyes due to slow activation rate, slow fading (bleeching)rate, and low activation intensity.

Nonetheless, there are several existing methods to incorporatephotochromic properties into lenses made from materials such aspolycarbonate. One method involves applying to the surface of a lens acoating containing dissolved photochromic compounds. For example,Japanese Patent Application 3-269507 discloses applying a thermosetpolyurethane coating containing photochromic compounds on the surface ofa lens. U.S. Pat. No. 6,150,430 also discloses a photochromicpolyurethane coating for lenses.

Another method involves coating a lens with a base coating. An imbibingprocess described in U.K. Pat. No. 2,174,711 or U.S. Pat. No. 4,968,454is used to imbibe a solution containing photochromic compounds into thebase coating material. The most commonly used base material ispolyurethane.

However, the two methods described above, which involve coating the lensafter it is molded, have significant shortcomings. For example,typically a coating of about 25 μm or more is needed to incorporate asufficient quantity of photochromic compounds into the base in order toprovide the desired light blocking quality when the compounds areactivated. This relatively thick coating is not suited for applicationon the surface of a segmented, multi-focal lens because an unacceptablesegment line and coating thickness nonuniformity around the segment lineare produced, and the desirable smooth surface quality is affected.

Lenses made from plastic materials such as polycarbonate are produced byan injection molding process and insert (also known as in-molddecoration) injection molding is used to incorporate photochromicproperties into the lenses. Insert injection molding is a processwhereby a composition is injection molded onto an insert in the moldcavity. For example, as disclosed in commonly assigned U.S. Pat. No.6,328,446, a photochromic laminate is first placed inside a mold cavity.Polycarbonate lens material is next injected into the cavity and fusedto the back of the photochromic laminate, producing a photochromicpolycarbonate lens. Because the photochromic function is provided by athin photochromic layer in the laminate, it is practical to makephotochromic polycarbonate lenses with any kind of surface curvature bythe insert injection molding method.

Transparent resin laminates with photochromic properties have beendisclosed in many patents and publications, for example, Japanese PatentApplications 61-276882, 63-178193, 4-358145, and 9-001716; U.S. Pat. No.4,889,413; U.S. Patent Publication No. 2002-0197484; and WO 02/093235.The most commonly used structure is a photochromic polyurethane hostlayer bonded between two transparent resin sheets. Although the use ofpolyurethane as a photochromic host material is well known, photochromicpolyurethane laminates designed especially for making photochromicpolycarbonate lenses through the insert injection molding method areunique.

Problems associated with conventional insert injection moldingtechniques in the manufacture of photochromic lens are polyurethanebleeding and poor replication of segment lines. “Bleeding” occurs fromthe deformation of the polyurethane layer during processing. Inparticular, bleeding occurs when the polyurethane layer melts andescapes from its position between the two transparent sheets of thelaminate during the injection molding process. The inventors havediscovered that bleeding most frequently results from an excess amountof polyurethane and from using too soft a material. The inventors havealso discovered that poor replication of segment lines occurs when thelayer of polyurethane is too thick and movement of the laminate occursas pressure from the mold is applied.

In order to prevent the bleeding problem, it is preferred to have thepolyurethane cross-linked. However, cross-linked polyurethane, oncemade, is difficult to be laminated between transparent resin sheets. Aconvenient method to incorporate cross-linked polyurethane is to startwith a liquid polyurethane system such as the one described in U.S.Patent Publication No. 2002-0197484. To make the laminate efficiently, aweb coat-laminate line such as the one described in Japan Patent LaidOpen 2002-196103, is usually used. The state of the art coatingequipment is capable of coating a uniform layer of liquid polyurethanemixture. However, this layer will only be partially solidified (orcured) at the moment of in-line lamination. Any possible surface defectsof resin sheet and lamination rollers are easily transferred to the softpolyurethane layer during lamination. The most often seen defects in thepolyurethane layer include thickness un-evenness across the web and thinspots due to uneven pressure at lamination or improper handling. Inorder to have the polyurethane layer firm enough to withstand thenecessary pressure during lamination, it needs to be cured for a certainamount of time, which slows down the processing or renders the continuesweb coating-laminating impossible.

Therefore, the need exists to overcome the problems and shortcomingsassociated with existing polyurethane laminates having photochromicproperties and methods of making these laminates.

BRIEF SUMMARY OF THE INVENTION

The need and shortcomings of the existing laminates and methods ofmanufacturing these laminates are met by the polyurethane laminate andmethod in accordance with the present invention.

It is an object of the present invention to provide a transparentphotochromic polyurethane laminate that has improved thicknessuniformity and surface smoothness, so that the darkness or lighttransmission at the activated state is uniform.

It is another object of the present invention to provide a photochromicpolyurethane laminate that exhibits dimensional stability under hightemperature and high pressure, so that it can be used to produce aplastic photochromic lens though an insert injection molding process.

The objects are achieved by the transparent photochromic polyurethanelaminate in accordance with the present invention. One embodiment of thepresent invention comprises a polyurethane layer including photochromiccompounds having first and second sides, a front transparent resin sheetis bonded to the first side of the polyurethane photochromic layer, anda back transparent resin sheet is bonded to the second side of thepolyurethane photochromic layer. The front and back transparent resinsheets may be bonded to the polyurethane layer with or withoutadditional adhesive such as epoxies and the acrylate types. The frontand back transparent resin sheets are preferably made of the samematerial as the lens base. That is, if the lens base material ispolycarbonate, it is preferred to have polycarbonate resin sheets bondedto the polyurethane photochromic layer. If the lens base material iscellulose acetate butyrate, then it is preferred to have celluloseacetate butyrate resin sheets bonded to the polyurethane photochromiclayer. Any clear, transparent plastic resin may be used for the base andresin sheets, for example, polysulfones, polyacrylates andpolycycloolefins. The term “front resin sheet” means that the resinsheet is facing the mold cavity to duplicate the front (convex) surfaceof the whole lens. By the term “back”, we mean that the resin sheet isfacing the lens base. The term “lens base” means the portion of the lensthat is molded onto the laminate to form the main portion of the lens.

The objects of the present invention are further achieved by the carefuldesign of the polyurethane composition used to host the photochromicdyes. The polyurethane layer material comprises a) a solid thermoplasticpolyurethane, b) at least one aliphatic isocyanate-terminatedpolyurethane prepolymer, and c) at least one photochromic compoundselected from a group consisting of spiropyrans, spiroxizines, fulgides,fulgimides, and naphthopyrans. The thermoplastic polyurethane has atheoretical NCO index from 90 to 105, and a molecular weight (numberaveraged) of from 9,000 to 100,000. The isocyanate prepolymer has a NCOcontent of from 1.0% to 10.0%, by weight. The weight ratio of thethermoplastic polyurethane vs. the isocyanate prepolymer is in the rangefrom 1:9 to 9:1. The photochromic compound(s) counts for 0.1% to 5% ofthe total polyurethane, by weight.

To enhance the fatigue resistance of the photochromic compounds,stabilizers such as antioxidants, light stabilizers, and UV absorbersare added in the polyurethane layer.

The photochromic laminate is preferably made through a cast-laminationprocess. All components described above are dissolved in a suitablesolvent, cast on a release liner. After the solvent is evaporatedsubstantially, the thermoplastic polyurethane portion will provide thecast polyurethane film enough rigidity to go through the laminationprocess without any deformation. After lamination, the polyurethaneprepolymer will provide further curability by reacting with activehydrogen atoms in the system to enhance the dimensional stability of thepolyurethane layer under high temperature and high pressure.

Although the photochromic laminate according to this invention isespecially suitable for making photochromic polycarbonate lenses throughthe insert injection molding process, other non-limiting uses includephotochromic transparencies such as goggles and face shields.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a photochromic polyurethane laminatehaving two transparent resin sheets bonded to a photochromicpolyurethane layer formed by curing a mixture of a solid thermoplasticpolyurethane, at least one isocyanate prepolymer, at least onephotochromic compound, and a stabilizing system. The thermoplasticpolyurethane has a theoretical NCO index of from 90 to 105, and amolecular weight (number averaged) of from 20,000 to 100,000. Theisocyanate prepolymer has a NCO content of from 1.0% to 10.0%, byweight. The weight ratio of the thermoplastic polyurethane vs. theisocyanate prepolymer in the photochromic polyurethane composition is inthe range from 1:9 to 9:1. The photochromic compound(s) counts for 0.1%to 5% of the total polyurethane, by weight.

To enhance the fatigue resistance of the photochromic compounds,stabilizers such as antioxidants, light stabilizers, and UV absorbersare added in the polyurethane layer.

The photochromic laminate is preferably made through a cast-laminationprocess. All components described above are dissolved in a suitablesolvent, cast on a release liner. After the solvent is evaporatedsubstantially, the thermoplastic polyurethane portion will provide thecast polyurethane film enough rigidity to go through the laminationprocess without any deformation. After lamination, the polyurethaneprepolymer will provide further curability by reacting with activehydrogen atoms such as those of terminal hydroxyl groups, moisture,urethane groups, and urea groups in the system to enhance thedimensional stability of the polyurethane layer under high temperatureand high pressure.

Transparent Resin Sheets

The material used to make the transparent resin sheet is not limited solong as it is a resin with high transparency. In case the photochromicpolyurethane laminate of the present invention is incorporated into athermoplastic article such as a spectacle lens, the transparent resinsheets of the laminate is preferably of a resin material that isthermally fusible to the article base material so that the photochromiclaminate is tightly integrated with the article base when produced withthe insert injection molding process. Thus, it is more preferred to havesame kind of material for both the article base and the transparentresin sheets.

Suitable sheet resin materials include polycarbonate, polysulfone,cellulose acetate butyrate (CAB), polyacrylates, polyesters,polystyrene, copolymer of an acrylate and styrene, blends of compatibletransparent polymers. Preferred resins are polycarbonate, CAB,polyacrylates, and copolymers of acrylate and styrene. Apolycarbonate-based resin is particularly preferred because of hightransparency, high tenacity, high thermal resistance, high refractiveindex, and most importantly, and especially its compatibility with thearticle base material when polycarbonate photochromic lenses aremanufactured with the photochromic polyurethane laminate of the presentinvention and the insert injection molding process. A typicalpolycarbonate based resin is polybisphenol-A carbonate. In addition,examples of the polycarbonate based resin include homopolycarbonate suchas 1,1′-dihydroxydiphenyl-phenylmethylmethane,1,1′-dihydroxydiphenyl-diphenylmethane,1,1′-dihydroxy-3,3′-dimethyldiphe-nyl-2,2-propane, their mutualcopolymer polycarbonate and copolymer polycarbonate with bisphenol-A.

While the thickness of a transparent resin sheet is not particularlyrestricted, it is typically 2 mm or less, and preferably 1 mm or lessbut not less than 0.025 mm.

Thermoplastic Polyurethane

As the thermoplastic polyurethane, it is preferably made from adiisocyanate, a polyol, and a chain extender. Thermoplasticpolyurethanes of this kind are known and may be obtained, for example,in accordance with U.S. Pat. Nos. 3,963,679 and 4,035,213, thedisclosures of which are incorporated herein by reference.

The thermoplastic polyurethane used in the present invention isparticularly prepared from a composition comprising a) an aliphaticisocyanate having a functionality of 2, b) at least one high molecularweight polyol having a nominal functionality of 2 and a molecular weightof from 500 to 6000 g/mole, preferably from 700 to 3000 g/mol, andcounting for from about 50% to about 98% by weight, preferably from 70%to 95%, of the total isocyanate reactive species in the composition, andc) at least one low molecular weight diol having a molecular weight offrom 62 to 499, and counting for from about 2% to about 50% by weight,preferably from 5% to 30%, of the total isocyanate reactive species inthe composition.

Polyols

The polyols of the present invention are those conventionally employedin the art for the preparation of polyurethane cast elastomers.Naturally, and often times advantageously, mixtures of such polyols arealso possible. Examples of the suitable polyols include polyetherpolyols, polyester polyols, polyurethane polyols, polybutadiene polyol,and polycarbonate polyols, while polyether and polyester types arepreferred.

Included among suitable polyether polyols are polyoxyethylene glycol,polyoxypropylene glycol, polyoxybutylene glycol, polytetramethyleneglycol, block copolymers, for example, combinations of polyoxypropyleneand polyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethyleneglycols, poly-1,4-tetramethylene and polyoxyethylene glycols, andcopolymer glycols prepared from blends or sequential addition of two ormore alkylene oxides. The polyalkylene polyether polyols may be preparedby any known process such as, for example, the process disclosed inEncyclopedia of Chemical Technology, Vol. 7, pp. 257-262, published byInterscience Publishers, Inc. (1951), the disclosure of which isincorporated herein by reference.

Polyethers which are preferred include the alkylene oxide additionproducts of polyhydric alcohols such as ethylene glycol, propyleneglycol, dipropylene glycol, trimethylene glycol, 1,2-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, hydroquinone,resorcinol glycerol, glycerine, 1,1,1-trimethylol-propane,1,1,1-trimethylolethane, pentaerythritol, 1,2,6-hexanetriol,.alpha.-methyl glucoside, sucrose, and sorbitol. Also included withinthe term “polyhydric alcohol” are compounds derived from phenol such as2,2-bis (4-hydroxyphenyl)-propane, commonly known as Bisphenol A.

The suitable polyester polyols include the ones which are prepared bypolymerizing ε-caprolactone using an initiator such as ethylene glycol,ethanolamine and the like. Further suitable examples are those preparedby esterification of polycarboxylic acids. Further suitable polyesterpolyols include reaction products of polyhydric, preferably dihydricalcohols to which trihydric alcohols may be added and polybasic,preferably dibasic carboxylic acids. Instead of these polycarboxylicacids, the corresponding carboxylic acid anhydrides or polycarboxylicacid esters of lower alcohols or mixtures thereof may be used forpreparing the polyesters. The polycarboxylic acids may be aliphatic,cycloaliphatic, aromatic and/or heterocyclic and they may besubstituted, e.g., by halogen atoms, and/or unsaturated. The followingare mentioned as examples: succinic acid; adipic acid; suberic acid;azelaic acid; sebacic acid; phthalic acid; isophthalic acid; trimelliticacid; phthalic acid anhydride; tetrahydrophthalic acid anhydride;hexahydrophthalic acid anhydride; tetrachlorophthalic acid anhydride,endomethylene tetrahydrophthalic acid anhydride; glutaric acidanhydride; maleic acid; maleic acid anhydride; fumaric acid; dimeric andtrimeric fatty acids such as oleic acid, which may be mixed withmonomeric fatty acids; dimethyl terephthalates and bis-glycolterephthalate. Suitable polyhydric alcohols include, e.g., ethyleneglycol; propylene glycol-(1,2) and -(1,3); butylene glycol-(1,4) and-(1,3); hexanediol-(1,6); octanediol-(1,8); neopentyl glycol;(1,4-bis-hydroxymethylcyclohexane); 2-methyl-1,3-propanediol;2,2,4-trimethyl-1,3-pentanediol; triethylene glycol; tetraethyleneglycol; polyethylene glycol; dipropylene glycol; polypropylene glycol;dibutylene glycol and polybutylene glycol, glycerine andtrimethlyolpropane. A preferred polyester polyol is polycaprolactonepolyol having an average molecular weight from 500 to 6,000, andpreferably from 700 to 3,000.

Diols

Suitable diols are those polyols listed above having a functionality of2 and a molecular weight of from 62 to 499. Preferred diols are1,4-butane-diol and 1,3-propane-diol.

Isocyanates

The diisocyanate component is preferably an aliphatic diisocyanate. Thealiphatic diisocyanate is selected from the group consisting of1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate,2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylenediisocyanate, cyclohexane-1,3- and -1,4-diisocyanate,1-isocyanato-2-isocyanatomethyl cyclopentane,1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophoronediisocyanate or IPDI), bis-(4-isocyanatocyclohexyl)-methane,2,4′-dicyclohexylmethane diisocyanate, 1,3- and1,4-bis-(isocyanatomethyl)-cyclohexane,bis-(4-isocyanato-3-methylcyclohexyl)-methane,.alpha.,.alpha.,.alpha.′,.alpha.′-tetramethyl-1,3- and/or -1,4-xylylenediisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane,2,4- and/or 2,6-hexahydrotoluylene diisocyanate, and mixtures thereof.Bis-(4-isocyanatocyclohexl)-methane is the preferred diisocyanate inoccurrence with the method of the present invention.

The polymerization process to make the thermoplastic polyurethane can becarried out in one-pot fashion, that is, all starting materials areinitially added into the reaction vessel. The polymerization process canalso be carried out with a prepolymer approach. That is, a polyurethaneprepolymer terminated with isocyanate groups is first obtained byreacting a stoichiometrically in excess diisocyanate with a polyol.Suitable equivalent ratio of diisocyanate to polyol in the presentinvention is from 1.2:1.0 to 8.0:1.0. A chain extender of diol is thenmixed with the prepolymer to complete the reaction. The NCO index of thethermoplastic polyurethane, formed from the quotient, which ismultiplied by 100, of the equivalent ratio of isocyanate groups to thesum of the hydroxyl groups of polyol and chain extender is within arange of 90 to 105, preferably between 92 and 101.

Catalysts such as organotin or other metallic soaps may be added in themixture to make a thermoplastic polyurethane. Example catalysts includedibutyltin dilaurate, stannous octoate, and cobalt naphthenate.

Isocyanate Prepolymer

The isocyanate prepolymer used in the photochromic polyurethanecomposition of the present invention is prepared in the same way as theprepolymer used to prepare the thermoplastic polyurethane in aprepolymer method described above. Preferably, the polyol and theisocyanate used to make the isocyanate prepolymer is the same as thepolyol to make the thermoplastic polyurethane. More preferably, theisocyanate is an aliphatic diisocyanate described in the previoussections, and the polyol is a polyester polyol having a molecular weightbetween 700 and 3,000. The molecular weight (number averaged) of theisocyanate prepolymer is preferably between 1,000 and 6,000, and morepreferably between 1,500 and 4,000. As an isocyanate group terminatedprepolymer, its NCO content is between 1.0% and 10.0%, preferablybetween 2.0% and 8.0%.

When mixing the isocyanate prepolymer and the thermoplastic polyurethanetogether, the mixing ratio by weight is in the range from 1:9 to 9:1,preferably from 1:3 to 3:1.

Photochromic Compounds

Suitable photochromic compounds in the context of the invention areorganic compounds that, in solution state, are activated (darken) whenexposed to a certain light energy (e.g., outdoor sunlight), and bleachto clear when the light energy is removed. They are selected from thegroup consisting essentially of benzopyrans, naphthopyrans,spirobenzopyrans, spironaphthopyrans, spirobenzoxzines,spironaphthoxazines, fulgides and fulgim ides. Such photochromiccompounds have been reported which, for example, in U.S. Pat. Nos.5,658,502, 5,702,645, 5,840,926, 6,096,246, 6,113,812, and 6,296,785;and U.S. patent application Ser. No. 10/038,350, all commonly assignedto the same assignee as the present invention and all incorporatedherein by reference.

Among the photochromic compounds identified, naphthopyran derivativesare preferred for optical articles such as eyewear lenses. They exhibitgood quantum efficiency for coloring, a good sensitivity and saturatedoptical density, an acceptable bleach or fade rate, and most importantlygood fatigue behavior. These compounds are available to cover thevisible light spectrum from 400 nm to 700 nm. Thus, it is possible toobtain a desired blended color, such as neutral gray or brown, by mixingtwo or more photochromic compounds having complementary colors under anactivated state.

More preferred are naphtho[2,1b]pyrans and naphtho[1,2b]pyransrepresented by the following generic formula:

Substituents on various positions of the aromatic structure are used totune the compounds to have desired color and fading rate, and improvedfatigue behavior. For example, a photochromic dye may contain apolymerizable group such as a (meth)acryloyloxy group or a (meth)allylgroup, so that it can be chemically bonded to the host material throughpolymerization.

The quantity of photochromic compound(s) incorporated into thepolyurethane layer of the present invention is determined by the desiredlight blockage in the activated state and the thickness of thepolyurethane layer itself. The preferred outdoor visible lighttransmission of sunglasses is preferably between 5% and 50%, morepreferably between 8% and 30%, most preferably between 10% and 20%.Preferably, the amount of total photochromic substance incorporated intoor applied on the polyurethane layer may range from about 0.1 wt. % toabout 5 wt. % of the total polyurethane, and more preferably from about0.5 wt. % to about 3.0 wt. %. If the thickness of the polyurethane layeris 100 μm, between about 0.5 wt. % to about 1 wt. % of photochromiccompound(s) is needed to achieve an outdoor light transmission ofbetween 10% and 20%. The amount of photochromic compound(s) needed isinversely proportional to the thickness of the polyurethane layer. Inother words, to achieve the same outdoor light transmission the thickerthe polyurethane layer, the lower the concentration of photochromiccompound(s) needed. The concentration of the photochromic compound(s)also depends on the color intensity of the photochromic compound(s) atthe activated state.

Stabilizers

Additives such as antioxidants and light stabilizers are incorporatedinto the polyurethane layer in order to improve the fatigue resistanceof the photochromic compounds. Hindered amines are usually used as lightstabilizers, and hindered phenols are usually used as antioxidants.Preferred hindered amine light stabilizers include,bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-sebacate, or a condensationproduct of 1,2,2,6,6-pentamethyl-4-piperidinol, tridodecyl alcohol and1,2,3,4-butanetetra caboxylic acid as tertiary hindered amine compounds.Preferred phenol antioxidants include,1,1,3-tris(2-methyl-4-hydorxy-5-t-butylphenyl)butane,tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxy-phenyl)propionate]methane,and1,3,5-tris(3,5-di-t-butyl-4-hyroxybenzyl)-1,-3,5-triazine-2,4,6-(1H,3H,5H)-trione.Phenol antioxidants that contain 3 or more hindered phenols arepreferable.

Process to Make the Laminate

A photochromic laminate having a polyurethane layer in between twotransparent resin sheets in accordance with the present invention may beproduced through a variety of processes. Depending on the nature of thestarting material to the polyurethane, processes such ascasting-lamination (also referred to in the art as coating-lamination),and extrusion-lamination may be used.

To the photochromic polyurethane composition of the present invention, anovel casting-lamination process has been developed by the inventors.The process essentially comprises: a) preparing a solvent castingsolution by dissolving a solid thermoplastic polyurethane, at least oneisocyanate polyurethane prepolymer, at least one photochromic compound,and optional stabilizers in a proper solvent; b) cast the solution on arelease liner film; c) remove the solvent from the cast film to asubstantially dry state to form a photochromic polyurethane film; d)transfer-laminate the photochromic polyurethane film between twotransparent resin sheets; e) cure the photochromic polyurethane film,thereby forming a photochromic polyurethane laminate.

To cast a photochromic polyurethane film, a thermoplastic polyurethane,an isocyanate prepolymer, selected photochromic compounds and othernecessary additives are first dissolved in a suitable solvent or in amix of solvents to form a cast solution. The solid concentration in sucha solution is usually 15% to 50%, by weight, and the solution has aviscosity suitable for coating. For example, suitable viscosity of thecast solution for using a slot die method is within the range from 500cPs to 5000 cPs. Examples of suitable solvents that may be used todissolve polyurethanes include cyclohexane, toluene, xylene and ethylbenzene, esters such as ethyl acetate, methyl acetate, isopropylacetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, isoamylacetate, methyl propionate and isobutyl propionate, ketones such asacetone, methylethyl ketone, diethyl ketone, methylisobutyl ketone,acetyl acetone and cyclohexyl ketone, ether esters such as cellosolveaetate, diethylglycol diaetate, ethyleneglycol mono n-butyletheracetate, propylene glycol and monomethylether acetate, tertiary alcoholssuch as diacetone alcohol and t-amyl alcohol and tetrahydrofuran. Ethylacetate, methyl ethyl ketone, cyclohexane, tetrahydrofuran, toluene andcombinations thereof are preferable.

The solution is then cast on a release liner by using a method known tothose skilled in the art, such as slot-die, knife-over-roll,reverse-roll, gravure, etc. Slot die and knife-over-film are referred.Slot die method is especially preferred due to its capability to handlewide range of solution viscosity and to cast uniform films. A releaseliner may consist of a base film and a release coating or simply a filmitself. Films with surface energy low enough to provide easy release ofthe cast film can be used by itself. Examples include low energypolyolefins and fluoropolymers. Most commercially available releaseliners are based on polyester film coated with a release coating. Therelease coating has a proper surface energy so that a cast solution orcoating forms a uniform film (e.g., without beading) on it. At the sametime the release coating does not provide good adhesion to the driedfilm so that the film can be easily peeled off. Release coatings includesilicone (siloxane) based and non-silicone base such as fluoropolymers.A liner based on polyester (PET) with cured siloxane release coating ispreferred due to the dimensional stability, flatness, handling, solventresistance, low cost. Suitable liners should have a thickness of from 25micrometers to 130 micrometers.

The wet photochromic polyurethane film cast on the release liner issequentially dried in a forced air oven system. The solvent will besubstantially evaporated so that the solvent retention in thephotochromic polyurethane film is low enough to not cause any defects(e.g., bubbling) in the future laminate. The solvent retentionpreferably is less than 2 wt. %, more preferably less than 1 wt. %, andmost preferably less than 0.5 wt. %. Conventional methods such as hotair dryers may be used to evaporate the solvent before lamination. Thedrying conditions, such as temperature and air flow rate in the oven,for a desired solvent retention value depends on the nature of thesolvent, the thickness of the cast film, the type of the release liner,and the web speed. The drying conditions should not be so aggressive tocause any surface defects in the cast film. Example defects are blisters(bubbles) and orange peel. Preferably, the drying oven system hasmulti-zones whose drying conditions are controlled separately.

The thickness of the dried photochromic polyurethane layer is from about5 micrometers to about 150 micrometers. For using the photochromiclaminate in an insert injection molding process to make plasticphotochromic lenses, the thickness of the photochromic polyurethane ispreferably between 5 micrometers and 80 micrometers. The thicknessvariation of the photochromic polyurethane layer should be controlled inorder to produce a uniform light blockage at the activated state. Athickness variation of less than 15% over the width of the laminate isrequired and preferably less than 10% and more preferably less than 5%.

The transfer-lamination of the dried photochromic polyurethane film totwo transparent resin sheets to form a laminate of the polyurethane filmbetween the two resin sheets, may be done by either a sequentiallamination process or an in-line lamination process. In a sequentiallamination process, the dried polyurethane film on the release liner isfirst laminated to the first transparent resin sheet through a firstlamination station. The semi-laminate consisting of the release liner,the polyurethane film, and the resin sheet, is then wound up on a core.The wind is then brought to a second lamination station where therelease liner is peeled off and the second transparent sheet islaminated to the polyurethane film to form the final photochromicpolyurethane laminate. The first and the second lamination stations maybe the same one. The lamination may be conducted between two chromecoated steel rolls or between one steel roll and one rubber roll,although the later is preferred.

According to the findings of the inventors, an in-line laminationprocess is more preferred. In such a process, the second transparentresin sheet is immediately laminated to the semi-laminate without firstwinding the semi-laminate. The in-line lamination may be done with twotwo-roll lamination stations, or more conveniently be conducted on onethree-roll setup in which the first roll and the second roll form afirst nip, and the second roll and the third roll form a second nip. Thedried polyurethane film on the release liner is first laminated to thefirst transparent resin sheet through the first nip. Without forming andwinding a semi-laminate, the release liner is peeled off, and the secondtransparent resin sheet is immediately laminated to the exposed side ofthe polyurethane film on the first transparent resin sheet, through thesecond nip. This in-line lamination process will significantly increasethe productivity. It also eliminates an extra winding step and reducesthe possibilities of defects in the polyurethane film associated withthe winding step. Example defects are de-lamination between thepolyurethane film and the transparent resin sheet, impressions in thepolyurethane film caused by possible external particles under windingpressure.

The photochromic polyurethane laminate thus formed according to thepresent invention needs to be cured before application. The curing ispreferably carried in two stages: a) ambient curing for 1 day to 1 week,b) post curing at elevated temperature of from 50° C. to 130° C. for 8hours to 1 week.

If the solvent selected to dissolve the photochromic polyurethanecomposition does not whiten the transparent resin sheet, a direct caston the resin sheet may be employed. In this case, a simple two-rolllamination setup is acceptable for making a photochromic polyurethanelaminate.

In an alternative process, the photochromic layer from a thermoplasticpolyurethane and isocyanate-terminated polyurethane prepolymer may beco-extruded utilizing a single- or twin-screw extruder. The extrudedphotochromic polyurethane film will then be immediately hot-laminatedbetween two transparent resin sheets to form the photochromicpolyurethane laminate. The photochromic compounds and other additivesmay be incorporated into the polyurethane during the resin synthesisstage or melt-mixed prior to extrusion.

Although the photochromic laminate according to the present invention isespecially suitable for making photochromic polycarbonate lenses throughthe insert injection molding process described in commonly assigned U.S.Pat. No. 6,328,446, it can also be used as-is for other photochromictransparencies such as goggles and face shields. The photochromiclaminate may also be incorporated into other types of eyewear lensessuch as cast resin lenses with a process described in U.S. Pat. No.5,286,419.

The photochromic polyurethane laminate in accordance with the presentinvention will now be illustrated with reference to the followingexamples, which are not to be construed as a limitation upon the scopeof the invention in any way.

In the examples, all values are expressions of weight %. CR49 and CR59are tradenames of photochromic dyes available from Corning Corp.Grey-762 is proprietary grey photochromic dye. Irganox-1010 as anantioxidant, Tinuvin-144 and Tinuvin-765 as light stabilizers areavailable from CIBA (Tarrytown, N.Y., US).

To visually evaluate the activation and the photochromic polyurethanelayer uniformity, a photochromic laminate or lens was exposed to UVirradiation (12 mw/m2) for 5 minutes.

Example 1

Preparation of Isocyanate Polyurethane Prepolymer A: In a 3-necked flaskequipped with an overhead stirrer, thermocouple, and a vacuum adapter,393.5 g (3 equivalents) of 4,4′-dicyclohexylmethanediisocyanate (H12MDI,available from Bayer as Desmodur W) was charged into the reactor andstirred at ambient temperature. 1000 g (2 equivalents) of apolycaprolactone diol having an OH number of 112 mg KOH/g and a numberaverage molecular weight of about 1000 g/mole (available from DowChemical as Tone™ 2221) was preheated in an oven to 80° C. and added tothe reactor. The mixture was allowed to stir for about 15 minutes,before adding 6 g of dibutyltin dilaurate catalyst (available from AirProducts as T-12). The reaction flask was evacuated (<0.1 mm HG) andheld at 90° C. for 6 hours. An aliquot of the prepolymer was withdrawnand titrated for isocyanate content using standard n-butyl aminetitration. The isocyanate content was found to be 2.92% (theory; 3.0%).

Example 2

Preparation of Isocyanate Polyurethane Prepolymer B: In a 3-necked flaskequipped with an overhead stirrer, thermocouple, and a vacuum adapter,613.0 g (4.67 equivalents) of 4,4′-dicyclohexylmethanediisocyanate(H12MDI, available from Bayer as Desmodur W) was charged into thereactor and stirred at ambient temperature. 1000 g (2 equivalents) of apolycaprolactone diol having an OH number of 112 mg KOH/g and a numberaverage molecular weight of about 1000 g/mole (available from DowChemical as Tone™ 2221) was preheated in an oven to 80° C. and added tothe reactor. The mixture was allowed to stir for about 15 minutes,before adding 8 g of dibutyltin dilaurate catalyst (available from AirProducts as T-12). The reaction flask was evacuated (<0.1 mm HG) andheld at 90° C. for 6 hours. An aliquot of the prepolymer was withdrawnand titrated for isocyanate content using standard n-butyl aminetitration. The isocyanate content was found to be 6.75% (theory; 7.0%).

Preparation of Thermoplastic Polyurethane: A thermoplastic polyurethanehaving a theoretical NCO index of 95 was prepared as following. Theisocyanate prepolymer B (927.2 g) prepared in Example 2 was heated invacuo (<0.1 mm HG) with stirring to 80° C. and 1,4-butane-diol (72.8 g)as the chain extender and 3 g of dibutyltin dilaurate catalyst werecombined with the prepolymer while keeping stirring. The mixture wasstirred for 30 seconds and subsequently poured into a Teflon lined tray.The tray containing the casting was cured in an oven at 85° C. for 24hours.

Example 4

A solution was first made by dissolving 4 g of the thermoplasticpolyurethane prepared in Example 3 in 16 g of anhydrous tetrahydrofuran.To the solution was further added 4 g of the isocyanate prepolymerprepared in Example 1, 0.14 g of CR49 dye, 0.02 g CR59 dye, 0.17 g eachof Irganox-1010, Tinuvin-144, and Tinuvin-765. The mixture was stirredat room temperature for 3 hours before cast on an easy release liner(available from CPFilms as T-50) with draw bar targeting a 38 micrometerdry film thickness. The solvent in the cast film was evaporated at 60°C. for 5 minutes with airflow above the film. The dried film wastransfer-laminated between two 0.3 mm thick polycarbonate sheets(available from Teijin as PC-1151) with a bench top roller laminator.After 4 days under ambient, the laminate was cured at 70° C. for 3 days.

The laminate was cut into a 76 mm disc and used to make a segmentedmulti-focal polycarbonate photochromic lens. After the insert injectionmolding process with common molding parameters, the finished lens had anacceptable thin, crisp segment line. No polyurethane bleeding from thelaminate was observed. The lens showed quick and uniform photochromicactivation. No any lamination defects were observed.

Example 5

A solution having 28.2% solid, was first prepared by dissolving 1950 gof the thermoplastic polyurethane prepared as in Example 3 in 7550 g ofanhydrous tetrahydrofuran. To the solution was further added 780 g ofthe isocyanate prepolymer prepared as in Example 1, 59 g each of “762”dye, Irganox-1010, Tinuvin-144, and Tinuvin-765. The mixture was stirredat room temperature for 3 hours then set overnight before cast on aneasy release liner (available from Saint-Gobain as 8310) at a web speedof 5.5 feet per minute in a pilot coater equipped with a slot die, atwo-zone drying oven, and a three-roll lamination station. The solventin the cast film was evaporated at 70° C. for 1 minute and 120° C. foranother minute with forced airflow above the film. The dried film was 38micrometer thick and had a solvent retention of 0.1%. It wastransfer-laminated between two 0.3 mm thick polycarbonate sheets(available from Teijin as PC-1151) with an in-line process (withoutwinding the semi-laminate of the release liner, polyurethane film, andthe first polycarbonate sheet). After 4 days in ambient (22° C. and35%˜50% RH), the laminate was cured at 70° C. for 3 days.

The laminate was cut into 76 mm discs and used to make a segmentedmulti-focal polycarbonate photochromic lenses. After the insertinjection molding process with common molding parameters, the finishedlens had an acceptable thin, crisp segment line. No polyurethanebleeding from the laminate was observed. The lens showed quick anduniform photochromic activation. No any lamination defects wereobserved.

Example 6

A solution having 35.3% solid, was first prepared by dissolving 1950 gof the thermoplastic polyurethane prepared as in Example 3 in 7742 g ofanhydrous tetrahydrofuran. To the solution was further added 1950 g ofthe isocyanate prepolymer prepared as in Example 1, 68 g of CR49 dye, 10g CR59 dye, 85 g each of Irganox-1010, Tinuvin-144, and Tinuvin-765. Themixture was stirred at room temperature for 3 hours then set overnight,then cast directly on a first 0.3 mm thick polycarbonate sheet(available from Teijin as PC1151) at a web speed of 5.5 feet per minutein a pilot coater equipped with a slot die, a two-zone drying oven, anda three-roll lamination station. The solvent in the cast film wasevaporated at 94° C. for 1 minute and 127° C. for another minute withforced airflow above the film. The dried film was 25 micrometer thickand had a solvent retention of 0.1%. A second 0.3 mm thick polycarbonatesheet was laminated on the exposed side of the dried polyurethane filmon the first polycarbonate sheet. After 4 days in ambient (22° C. and35% 50% RH), the laminate was cured at 70° C. for 3 days. The laminateobtained was clear. No solvent whitening on the polycarbonate sheets wasseen.

Comparison Example 1

To 10 g of Hysol® (Loctite) U-10FL urethane adhesive resin are dissolved1.5% of “762” dye, 2.0% of Tinuvin 144, and 2.0% of Tinuvin 765. Then,9.1 g of Hysol® U-10FL urethane adhesive hardener is mixed in to form aliquid adhesive.

The adhesive was coated with a draw bar directly on a polycarbonatesheet (0.3 mm thick, available from Teijin as 1151) to form a 38micrometer cast film. Another polycarbonate sheet was laminated onto theadhesive through a bench top roller laminator. Some adhesive wassqueezed out. The laminate was allowed to cure at room temperatureovernight, then is post cured at 65° C. for 10 hours.

When the photochromic laminate was activated, thin spots (lightlyactivated due to thinner spots in the polyurethane layer) andnon-uniformity of activation due to thickness gradient across thelaminate were observed.

Comparison Example 2

Example 4 was followed, except the isocyanate prepolymer was neglected.The photochromic polyurethane layer was 38 micrometers thick. Thelaminate showed uniform photochromic activation. No lamination defectswere observed. However, when molded into a polycarbonate lens as inExample 4, severe polyurethane bleeding was observed at the edge of thelaminate.

The foregoing detailed description of the preferred embodiments of theinvention has been provided for the purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise embodiments disclosed. Many modifications andvariations will be apparent to practitioners skilled in the art to whichthis invention pertains. The embodiments were chosen and described inorder to best explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the following claims and theirequivalents.

What is claimed is:
 1. A photochromic polyurethane layer prepared from amixture comprising a polyurethane, an isocyanate-terminated polyurethaneprepolymer, and a photochromic compound; the polyurethane having anumber average molecular weight from 9,000 to 100,000 and prepared froma composition comprising: an aliphatic diisocyanate comprising4,4′-dicyclohexylmethanediiso-cyanate; a polyester polyol; and a chainextender; the isocyanate-terminated polyurethane prepolymer preparedfrom a composition comprising: an aliphatic diisocyanate comprising4,4′-dicyclohexylmethanediiso-cyanate; and a polyester polyol; wherein amixing ratio of the polyurethane and the isocyanate-terminatedpolyurethane prepolymer by weight is in a range from 1:9 to 9:1 and saidpolyurethane comprises terminal hydroxyl groups, urethane groups andurea groups having active hydrogen atoms to react with saidisocyanate-terminated polyurethane prepolymer after lamination toprovide further curability of said photochromic polyurethane layer. 2.The photochromic polyurethane layer of claim 1 wherein the polyurethaneand the isocyanate-terminated polyurethane prepolymer are prepared fromthe same aliphatic diisocyanate.
 3. The photochromic polyurethane layerof claim 1 wherein the polyurethane and the isocyanate-terminatedpolyurethane prepolymer are prepared from the same polyester polyol. 4.The photochromic polyurethane layer of claim 1 wherein the polyurethaneand the isocyanate-terminated polyurethane prepolymer are prepared fromdifferent polyester polyols.
 5. The photochromic polyurethane layer ofclaim 1 wherein the polyurethane is prepared from a compositioncomprising a polycaprolactone.
 6. The photochromic polyurethane layer ofclaim 1 wherein the polyurethane is prepared from a compositioncomprising a polycaprolactone having a number average molecular weightof about 1000 grams per mole.
 7. The photochromic polyurethane layer ofclaim 1 wherein the polyurethane is prepared from a compositioncomprising a diol as a chain extender having a molecular weight in therange of approximately 62 to 499 grams per mole.
 8. The photochromicpolyurethane layer of claim 1 wherein the polyurethane is prepared froma composition comprising 1,4-butane-diol as the chain extender.
 9. Thephotochromic polyurethane layer of claim 1 wherein theisocyanate-terminated polyurethane prepolymer is prepared from acomposition comprising a polycaprolactone.
 10. The photochromicpolyurethane layer of claim 1 wherein the isocyanate-terminatedpolyurethane prepolymer is prepared from a composition comprising apolycaprolactone having a number average molecular weight of about 1000grams per mole.
 11. The photochromic polyurethane layer of claim 1wherein the polyester polyol has an OH number of 112 milligrams KOH pergram to prepare said polyurethane and said isocyanate-terminatedpolyurethane prepolymer.
 12. The photochromic polyurethane layer ofclaim 1 wherein the photochromic compound is selected from a groupconsisting of: benzopyrans, naphthopyrans, spirobenzopyrans,spironaphthopyrans, spirobenzoxzines, spironaph-thoxazines, fulgides andfulgim ides.
 13. A photochromic laminate for use in eyeglassescomprising: a first resin sheet; a second resin sheet; a photochromicpolyurethane film having a first side bonded to the first resin sheetand a second side bonded to the second resin sheet; the photochromicpolyurethane film prepared from a composition comprising: a polyurethanehaving a number average molecular weight from 9,000 to 100,000 andprepared from a composition comprising: an aliphatic diisocyanatecomprising 4,4′-dicyclohexylmethane-diisocyanate; a polyester polyol;and a chain extender; an isocyanate-terminated polyurethane prepolymerprepared from a composition comprising: an aliphatic diisocyanatecomprising 4,4′-dicyclohexylmethanediiso-cyanate; and a polyesterpolyol; and a photochromic compound; wherein a mixing ratio of thepolyurethane and the isocyanate-terminated polyurethane prepolymer byweight is in a range from 1:9 to 9:1 and said polyurethane comprisesterminal hydroxyl groups, urethane groups, and urea groups having activehydrogen atoms to react with said polyurethane prepolymer afterlamination to provide further curability of said photochromicpolyurethane film between the first resin sheet and the second resinsheet.
 14. The photochromic laminate of claim 13 wherein the first resinsheet and the second resin sheet comprise polycarbonate.
 15. Thephotochromic laminate of claim 13 wherein the polyurethane and theisocyanate-terminated polyurethane prepolymer are prepared from the samepolyester polyol.
 16. The photochromic laminate of claim 13 wherein thepolyurethane is prepared from a composition comprising apolycaprolactone having a number average molecular weight of about 1000grams per mole.
 17. The photochromic laminate of claim 13 wherein thephotochromic compound is selected from a group consisting of:benzopyrans, naphthopyrans, spirobenzopyrans, spironaphthopyrans,spirobenzoxzines, spironaph-thoxazines, fulgides and fulgim ides.